diff --git a/website/content/en/docs/reference/environment_variables.md b/website/content/en/docs/reference/environment_variables.md
index 177231095313c..06db13e50a2e2 100644
--- a/website/content/en/docs/reference/environment_variables.md
+++ b/website/content/en/docs/reference/environment_variables.md
@@ -57,6 +57,11 @@ You can escape environment variables by prefacing them with a `$` character. For
 example `$${HOSTNAME}` or `$$HOSTNAME` is treated literally in the above
 environment variable example.
 
+## Variable name restrictions
+
+Environment variable names used in interpolation are restricted to letters, digits plus `_`  and `.` characters. 
+Names containing other characters (such as hyphens `-`) will not be interpolated.
+
 ## Security Restrictions
 
 Vector prevents security issues related to environment variable interpolation by rejecting environment variables that contain newline